Bicycle suspension apparatus and related method

ABSTRACT

The invention is directed to a shock absorbing wheel suspension apparatus and related method. The preferred wheel suspension includes upper and lower rocker arms pivotably attached to a bicycle frame, rear shockstays pivotably attached to the upper and lower rocker arms, and a shock absorbing element. The preferred configuration of the wheel suspension results in improved performance through the desirable alignment of various force and torque lines over a wide range of loading conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. application Ser. No.09/623,210, filed Aug. 29, 2000, which was the National Stage ofInternational Application No. PCT/US99/04853, filed Mar. 2, 1999, whichclaims the benefit of U.S. Provisional Application No. 60/076,489, filedMar. 2, 1998, the contents of all of which in their entireties arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The invention is directed to a shock absorbing wheel suspensionapparatus and related method. Although the preferred embodiment isdescribed with respect to the rear suspension on a mountain bike,persons of ordinary skill in the art will understand that the inventionmay be readily utilized in other configurations and devices, especiallythose using chain drive power on a suspended wheel, including (by way ofexample and not by way of limitation) suspensions for motorcycles,tricycles, four-wheeled vehicles, and other vehicles.

[0003] The following table sets forth U.S. patents which may be materialto the patentability of the invention: U.S. Pat. No. Inventor Issued4,789,174 Lawwill December 1988 5,121,937 Lawwill June 1992 5,217,241Girvin June 1993 5,244,224 Busby September 1993 5,306,036 Busby April1994 5,409,249 Busby April 1995 5,441,292 Busby August 1995 5,474,318Castellano December 1995 5,509,679 Leitner April 1996 5,628,524 Klassenet al. May 1997 5,671,936 Turner September 1997 5,678,837 LeitnerOctober 1997

[0004] Also, a number of Internet websites currently display bicycleshaving wheel suspensions. Examples can be seen at the websites for thefollowing companies: Cyber Cyclery, Intense Cycles, Inc., GT Bicycles,Mountain Cycle, Schwinn, and Ventana Mountain Bikes.

[0005] Although current bicycle suspension designs typically includeshock absorption capabilities that are intended, among other things, toprovide comfort and safety and, ideally, to allow the tires to maintaincontact with the ground (even on uneven surfaces) and have traction onrough, steep climbs and descents, current designs have a number ofinherit faults or shortcomings.

[0006] Among other things, suspensions typically permit riders todescend with greater speed, control and comfort. Moreover, although thesuspension provides some benefits for climbing (and, as indicated,definitely provides important benefits to descending), many (if notmost) current designs are actually generally considered a hindrance toclimbing. During climbing, most prior art suspensions “suck” power (asdescribed below); the less kinetically efficient designs typically“suck” the most power during climbing. In addition, many prior artsuspension designs are so bulky or contorted that they add undesirableweight to the bicycle, which also “sucks” power from the rider,especially during climbing.

[0007] While some of the benefits provided by the invention might beachievable by using idler pulleys and other components, such approachespresumably would add weight (for the extra components) and theadditional drag of pulleys would of course require additional energy topropel (from the rider, the engine, etc.)

[0008] In addition, it would presumably be difficult (or evenimpossible) to utilize such a pulley system on a bicycle with otherwiseconventional industry standard components (gears, derailleurs, etc.). Inother words, such pulley approaches might not be able to use an“off-the-shelf” set of gears.

[0009] Several examples of these shortcomings are further discussedbelow.

[0010] 1. Pedaling Power Loss Due to Drive Torque Induced SuspensionMovement (“Torque Reactive” Suspensions).

[0011] All current bicycle rear suspensions of which the inventors areaware have a tendency to either compress or extend the rear suspensionwhen subjected to drive chain and wheel drive loads. Designs thatcompress the rear suspension cause the rider's power to be used forcompressing the shock absorber. The potential energy transferred to theshock absorber is dissipated as heat by the damping medium in the shockabsorber. Designs that extend the suspension under load waste power bylifting the mass of the bike and rider with each stroke. Designs thatattempt to exploit the chain loads to create torque against thesuspension create a binding action of the suspension under pedal torqueloads, which reduces ride quality and limits compliance-induced tractionunder hard pedaling.

[0012] Because an average human being can generate a maximum of aboutthree quarters (¾) horsepower and can do so for only a very short time,and can generate only about {fraction (1/10)}of a horsepower forextended periods, even small power losses can have a significant effecton the rider and the riding experience. In the designs described in thepreceding paragraph, potential energy is typically returned out of phaseto the pedals' and cranks' power stroke and is thus wasted as heatdissipated in the damper instead of power used to propel the bicycleforward.

[0013] In addition, suspension designs that are torque reactive feelmushy, sluggish and unresponsive to pedaling input.

[0014] Also, with a typical rear suspension design, the wheel follows anarc-like path when encountering a bump, forcing the wheel to bedisplaced in a forward as well as an upward direction (in contrast, andas shown by a comparison of FIGS. 3 and 6 of the preferred embodiment ofthe invention, as discussed below, the present invention provides muchmore nearly vertical wheel motion in response to bumps). Thus, whenabsorbing shocks, the prior art wheels must travel forward, frequentlyin an uphill direction. This increases the bump shock force transmittedto the sprung portion of the bicycle because the wheel is not movingperpendicularly away from the bump. It also requires more forward driveenergy from the rider to overcome the resulting “rearward” component ofsuch bump forces. Additionally, the suspensions will kickback thatmotion to the pedals, causing additional wasted energy and muscleirritation and premature fatigue from the uneven loading while pedaling.

[0015] This and other of the problems discussed herein are especiallyacute in human-powered devices such as bicycles, because the human powerplant typically provides such low RPM that the jacking or torquereaction happens (and is felt) with each revolution, rather then just“once” as might be experienced under acceleration from an internalcombustion engine, for example.

[0016] 2. Lock Up of the Rear Suspension Caused by Brake Induced Torque.

[0017] Almost all current art bicycle rear suspension designs place theanchor for their rear brakes (be it either a disc brake caliper ortraditional rim surface caliper type brakes) in a position where theapplication of brake force causes an extending force or “jacking” to beexerted on the rear suspension. This “jacking” force causes the rearsuspension to lose its effectiveness under heavy braking loads, as thejacking may lock out the suspension, and/or cause the rear of the biketo raise, forcing the rider forward and shifting the center of mass overthe front wheel, thereby causing instability of the bike and rider. Thisjacking can manifest itself as “wheel hop” and instability under heavybraking on rough surfaces.

[0018] Current suspension designs (as opposed to rigid rear linkages)create this unsafe (or at least difficult-to-control) jacking. Somedesigns utilizing a disc brake will counter these jacking forces byanchoring the brake forces with a separate member attached to the frameaway from the wheel suspension. Although this approach works toeliminate the brake “jacking” problem, it introduces additional weightand components (thus not lending itself to simple design), and may limitthe bicycle frame's kinetic responsiveness (which is one of the mainpoints of having a suspension in the first place). Other brakearrangements actually stiffen or even lock out the suspension whilebraking, even though arguably the most important time for suspensionfunctions are likely demanded while braking for obstacles or rough andtechnical terrain.

[0019] 3. Proper Shock Absorber Motion Ratio.

[0020] The motion ratio of the bike's shock absorber is critical toproper suspension operation. The motion ratio of the suspension bikescurrently on the market runs the range from rapidly rising to rapidlyfalling. There are major drawbacks as you move toward either end of thespectrum.

[0021] A very rapid rising rate causes the suspension to be too soft andactive in the initial part of the wheel travel, causing bobbing andwasting pedaling energy while quickly blowing through the initial travelon big bumps and “G-outs” (high load, long duration bump impulses),while eventually becoming non-compliant and harsh at later portions ofthe shock absorption motion. A rapid rising rate is caused by small“bell crank” shock rockers (or “rocker arms” or “rocker links” or “upperswingarms”) where the motion ratio is vastly changed through thesuspension stroke due to the great change in angle created by the smallrockers. Among other things, air shocks do not work well with risingrate suspensions as an air spring also has a rising rate which resultsin a very rapid rising rate.

[0022] A falling rate is the worst case scenario for a mountain bike'ssuspension. A falling rate suspension is initially stiff and gets softeras the suspension travel goes through its stroke. A falling ratesuspension is stiff and non-compliant on high frequency “stutter” bumps,while still blowing through the travel, bottoming out with great forceon big bumps.

[0023] A suspension with a slight falling rate can work fairly well whencombined with an air shock. Due to an air spring's progressive nature,the resulting combination is a nearly linear wheel “motion” rate.However, when a stiff spring is selected on a falling rate bike toprevent excessive bottoming, the suspension is very stiff and almostnon-existent on small or ripple (or “stutter”) bumps.

[0024] In contrast, and as discussed herein, the preferred embodiment ofthe current invention provides a frame having an almost linear(described herein as “progressively linear”) motion ratio. Persons ofordinary skill in the art will understand that perfect linearity wouldoccur if the first 1 inch “compression” movement of the bicycle wheelresulted in ¼ inch of compression of the shock member and every further1 inch increment of bicycle wheel “compression” movement likewisecorresponded to ¼ inch of shock member compression. A graph ofrepresentative prior art motion ratios, as well as the motion ratios forthe instant invention, is set forth in FIG. 3C. Because the preferred“frame” of the suspension behaves linearly, a user can “make” that sameframe function either with a generally linear or progressive motionratio, via the selection or adjustment of the shock absorbing member(which members come in a wide range of motion ratios andcharacteristics). As further described below, the preferred inventionincludes using longer rocker arms than any prior art of which theinventors are aware. The “rocker arm” is in fact so long that it is verynearly appropriate to call it an “upper” swingarm (in distinction fromthe “lower” swingarm element present in both the instant invention and(in broad concept) in many prior art designs. As indicated above, thoseprior art designs typically use a lower swingarm with the upper linkageformed by a “bell crank” or “rocker arm”.

[0025] This long “upper rocker arm” in the preferred embodiment of theinvention (along with the configuration and relative dimensions of thenose of that rocker arm) helps accomplish the desired alignment of thepivots in the linkage of the instant invention. This alignmentaccomplishes the linkage's desired tracking of the “instant center”(“IC”) so that it remains on or very near the chain tension line of thedrive chain (thereby reducing or eliminating undesirable chain torque).In the preferred embodiment, as described herein, the linkage's trackingkeeps the IC on (during normal operating “laden” [meaning having therider aboard the bicycle] mode of suspension) or very near (during anyother point of suspension travel) that chain torque line. No otherbicycle suspension (even other “four bar linkages”) of which theinventors are aware provides this beneficial tracking and/or theinitially laden orientation.

[0026] 4. Mechanically Simple, Elegant Design.

[0027] To address the various factors that determine performance ofwheel suspension, bicycle rear suspensions have evolved into a widerange of complicated, typically unreliable, “Rube Goldberg”-likedevices.

[0028] In addition, it is generally more economic if a design canutilize “standard” or “off-the-shelf” components, such as drive trainand brake components, rather than requiring those components to becustom designed and manufactured.

[0029] Existing devices typically suffer from one or more of theforegoing exemplary shortcomings, in various degrees and combinations.Examples of some of the most common rear suspension designs aredescribed below.

[0030] 1. Horst-Link McPherson Strut.

[0031] Pioneered by AMP research, and used by Lightspeed, RockyMountain, Intense, Turner, Specialized and others.

[0032] The basic operating principle of these devices is illustrated inU.S. Pat. No. 5,509,679 to Leitner. As shown there, the lower pivotingann or chainstay's pivot axis is located at or below the horizon pointof the tensioning run of the drive chain of the smallest chainring, anda rear swingarm pivot or lower link is located in front of the verticalaxis of the rear axle and below the horizontal axis of the rear axles.This location provides a binding action, mentioned above, that resistschain-induced “jacking” up and down movement of the suspension. Amongother things, the resistance to the chain-induced “jacking” isestablished by creating additional torques to counteract other torquesand thus results in the aforementioned “binding”.

[0033] Although this design is simple and lightweight, it has severalnegative performance indicators. While variations in designs utilizing a“Horst-Link” can incorporate to varying degrees some of the followingdesirable characteristics: somewhat non-pedaling force torque reactive,somewhat non-brake torque reactive, all “Horst Link” designs alsoexhibit to varying degrees the following undesirable characteristics(which one can generalize to have become accepted as the“state-of-the-art” in bicycle full-suspension designs): somewhatresponsive to pedal kickback from bump loads under pedaling force,reduced suspension activity due to mild to severe binding action of thesuspension geometry, and most Horst-Link, McPherson strut bicycle rearsuspensions suffer from a falling rate shock absorber motion ratio whichvaries greatly with frame size. The rear part of the bicycle frames arevery flexible, due to the fact that the shock absorber shaft is a majorstructural member of the linkage. Not only is the shock shaft a verypoor structural member (in part, typically, because of its smalldiameter), but the additional “linkage” loading on the shock also causesthe shock unit to heat up and sometimes bind, resulting in prematurewear and failure. Also, the suspension action is somewhat affected bypedal torque input. Mild binding action of the suspension under pedaltorque loads reduces ride quality and limits compliance-induced tractionunder hard pedaling. This is a significant disadvantage on steep roughclimbs. Brake torque and cornering loads cause shock bind. Brake loadcauses the suspension to jack upwards slightly. This design typicallyreacts to some degree to both brake- and pedal-induced torque loads,which loads vary dramatically with frame size and gear selection.

[0034] In contrast, and as more fully explained herein, the preferredembodiment of the invention prevents all these unwanted characteristics,specifically by utilizing the “upper swingarm” or rocker arm to help:(1) control the motion ratio of the frame, allowing for a selectablelinear or progressive shock motion ratio (accomplishable, among otherways, by selecting from a wide variety of off-the-shelf shock units);(2) reduce or eliminate wheel twist and similar forces, such as by usinga shockstay clevis (see FIGS. 2D-2I, for example) which holds the rearof the rockers firmly against lateral flex, along with the preferredrocker lateral brace at the midpoint and the preferred 8-mm bolts at thefour linkage pivots (calculations indicate that this upperswingarm/clevis/brace/bolts arrangement to be over 20% stiffer then thetubing used in most McPherson Strut designs; (3) have the linkagemembers' instant center track the chain torque of the bicycle throughoutthe suspension motion (thereby eliminating, by way of cancellation,rather then binding, or reducing chain torque energy waste, as discussedherein).

[0035] 2. High Single Pivot.

[0036] Used by Foes, Mountain cycle, Bolder, Pro Flex, Cannondale,Marin, and others.

[0037] The basic operating principle of these devices is illustrated inU.S. Pat. No. 5,217,241 to Girvin. The main pivot of the suspension islocated at a point slightly above the chainline of the large chainwheel.This provides a lifting moment to the suspension which is slight in thelarge chainring and greater in the smaller chainrings. The liftingmoment counteracts pedal and rider body movement-induced squat.

[0038] Although these designs can be somewhat simple in construction andsomewhat non-pedal-torque reactive in a certain chainring-gearcombinations, usually they are very pedal-torque reactive in thechainring farthest away horizontally from the pivot. In the smallchainrings, these constructions typically lift the bike and rider withan energy-wasting “inchworm” bobbing effect with each pedal stroke andits accompanying chain torque. These suspensions do not respond to bumploads under hard pedaling, as bump force must overcome the liftingmoment in order to move the wheels in reaction to a bump. Also, due totheir arc-like wheel path during shock absorption motion, the wheelbasedimension changes throughout the wheel's stroke, causing kickback whilepedaling. These designs are usually very brake-torque reactive, whichcauses the suspension to extend and lock out. These typically require abulky and sometimes heavy swingarm, as well as a huge overbuilt pivotand pivot supports, to maintain sufficient or desirable rigidity.

[0039] This prior art suspension is inexpensive to manufacture, but itsperformance is similarly limited, as described herein. It has only twoparts (front and rear), and one pivot. Companies having a sufficientlylarge advertising budget can charge a high price and have a big profitmargin on the suspension/bike, despite the marginal performance of the“high single pivot” suspension.

[0040] 3. Unified Rear Triangle.

[0041] Used by Trek, Gary Fisher, Klein, Schwinn, Ibis, and others.

[0042] This is a newer single pivot that was introduced once the buyingpublic figured out the shortcomings of the Single High Pivot discussedin the preceding section. Although the unified rear triangle is betterthan the Single High Pivot in most regards, it is not significantlybetter.

[0043] The basic operating principle of these devices is illustrated inU.S. Pat. No. 5,474,318 to Castellano. This design has a number ofpositive attributes: it provides correct natural frequency of thesuspension, thereby allegedly avoiding any pedal-force-produced bobbing;the entire bicycle drivetrain (including the cranks, and thus the pedalsand the entire bottom bracket assembly) is contained with the unsprungstructure of the rear suspension, thereby eliminating any chain-inducedsuspension bobbing and pedal kickback; using the rider's legs as part ofthe unsprung structure of the rear suspension purportedly allows therider to “adjust” the suspension on the fly by consciously stiffening orloosening his legs; positive shifting due to lack of suspension-inducedchain whip; it can be somewhat non-pedal-torque reactive depending onpivot location; provides a relatively smooth ride while seated, with nokickback effect through the pedals; and is a very simple design.

[0044] Nevertheless, suspensions of this type have some importantlimitations. They can be very pedal-torque-reactive depending on thepivot location. Bicycles with this suspension design usually suffer froma severe pedal-force-induced bobbing effect. The suspensioneffectiveness becomes compromised when a rider is standing, to a verylarge degree in some designs depending upon pivot location. This problemis substantial, in view of a rider's natural tendency to stand so thattheir legs can be used as shock absorbers and to improve their balancein extreme conditions. A unified rear triangle suspension becomes lesseffective while the rider is standing because the cranks and thus thepedals are attached to the rear “triangle” (which is the unsuspendedstructure of the bike frame), which is the opposite of what is needed(riders typically stand during extreme conditions, when shock absorptionis needed most). Depending on the pivot location, brake torque usuallycauses these designs to compress and pre-load or extend and lock up.This design also usually suffers from an extreme lack of rigidity duringout-of-line loading (such as occurs during cornering) due to using asingle pivot which has approximately the same moment arms with respectto the wheel's contact patch (the area where the tire contacts theground) as does the wheel's axis. When cornering or under similarloading conditions, that near identity of moment arms provides verylittle, if any, resistance to sideways twisting of the wheel. Because ofthis, the pivot, frame and swingarm must be overbuilt to maintainsufficient strength.

[0045] In contrast, the preferred embodiment of the invention has thecrank and pedals attached to the suspended frame member (the frontsection of the frame), so that the rider gets the benefits of being“suspended” (shock absorption, etc.) regardless of whether the rider issitting or standing. Moreover, the preferred embodiment of the inventionincludes a linkage with moment arms (with respect to the wheel's contactpatch) that provides substantial resistance to wheel twisting duringcornering and the like, without having to overbuild the size of thecomponents.

[0046] Perhaps as a result of the shortcomings of the unified reartriangle design, it has never (to the knowledge of the inventors) beenraced by a factory team of any of the major companies in the bicycleindustry.

[0047] 4. Multilink, Low Main Pivot.

[0048] Used by GT, Turner, Intense, KHS (the foregoing are all four-barlinkage designs) Ventana, Mongoose, and Diamond Back (the last threeutilize a swing or bell crank linkage).

[0049] The basic operating principle of these devices is illustrated inU.S. Pat. No. 5,441,292 to Busby and U.S. Pat. No. 5,678,837 to Leitner.The ride quality is improved by isolating bending moments from the fronttriangle by relocating the shock absorber to the rear link area of thesuspension. The shock absorbers' motion ratio is held close to lineardue to the positioning of the shock absorber and links. The wheeltravels in a near vertical path, instead of an arc, thus increasingshock absorbing efficiency and reducing energy wasting wheel fore andaft oscillations. Although some but not all four bar links are currentlythe most mature designs and are acknowledged by many people to be thebest functioning of the current designs (because, among other things, askilled designer has full control over shock motion ratio, brake torquereaction, and pedal torque reaction), there are still a number ofdisadvantages to the design. For example, currently most bikes usingthis design have been developed by trial and error with no clearunderstanding of all of the aspects of suspension function. Althoughsome prior art linkage designs may approach the functional performanceof the ICTR™ suspension (that of the present invention) in one aspect ofsuspension functionality, no single prior art design effectivelyaddresses all of the identifiable aspects of suspension function as doesthe ICTT. Among other things, prior art designs do not move the instantcenter to “track” and thereby cancel chain torque. Indeed, similar tothat mentioned above in connection with the ‘679 patent, the four-barsuspension system of the ‘837 patent tends to prevent “jacking” bycreating a binding action resulting from the interaction of the torquescreated to counteract the chain-induced torques, instead of cancelingchain torque by causing the instant center to track the chain torqueline, as does the preferred embodiment of the instant invention. Designsrange from relatively good (having superior suspension performancecharacteristics) to “Rube Goldberg” ridiculous. However, all of thecurrent multilink designs suffer from at least one of thepreviously-identified faults: pedal torque reactivity, brake torquereactivity, bump induced pedal kickback reactivity, binding orstiffening of the suspension under pedal loads, improper shock motionratio, and/or overly complex design. The relative flexibility of thisdesign concept has resulted in some bizarre functioning, ill-conceivedmachines. Among other things, more parts, more material, results inhigher manufacturing and maintenance costs and additional weight.

OBJECTS AND ADVANTAGES OF THE INVENTION

[0050] It is, therefore, an object of the invention to provide asuspension useful, for example, in connection with the rear wheel of abicycle such as a mountain bike, which overcomes all of the shortcomingsmentioned above.

[0051] Among other things, it is an object of the invention to provide awheel suspension in which the instant center of that suspensionsubstantially tracks the line of chain torque, thereby allowing thedrivetrain and power through the drivetrain, be it from the pedals orthe bumps, to be completely isolated from the suspension system and theforces it must respond to, and function from, including bumps, braking,etc. And at no time should the drivetrain's ability to conduct energy tothe rear wheel be negatively affected or have a negative effect on theindependent operation of the suspension function; thus reducing oreliminating chain torque force loss or effect due to one suspensionattached to the bicycle and canceling the undesirable loss of pedalstroke power or loss of suspension function at any time.

[0052] It is an additional object of the invention to provide a wheelsuspension in which, for any compression position of the suspension, theinstant center always falls between the maximum and minimum chain forcelines. This provides the opportunity for a rider to select a gear(between the range of maximum and minimum) that very closely or exactlyhits the IC, regardless of the compression position.

[0053] Another object of the invention is the provision of a suspensionthat isolates brake torque and its negative effects.

[0054] Yet another object of the invention is the provision of asuspension in which the shock motion ratio of the frame is linear orlinearly progressive.

[0055] A further object of the invention is the provision of a wheelsuspension in which “off-the-shelf” components may be readily used, suchas gear sets, drive trains, brakes, etc.

[0056] Another object of the invention is the provision of a suspensionin which a desirable amount of anti-squat is provided.

[0057] Yet a further object is the provision of a method of designingbicycle frames, which assists the designer in balancing variousattributes of the frame and bicycle and suspension. Such method caninclude, among others, steps of:

[0058] identifying the average (or constant, if in a single chain linesystem is used rather then a cluster of gears and several chainrings asdescribed in the preferred embodiment herein, which is currently thenorm or industry standard gearing systems for high performance bicycles)chain torque line of a given set of gears or of a single gears while thebike is in a laden position. Bikes are not ridden in other then a ladenposition, so good suspension design takes into account the weight of arider and the resulting normally laden suspension position;

[0059] selecting a location on that chain torque line that representsthe desired IC for the frame. Factors affecting this selection includethe amount of anti-squat (as discussed herein) one desires to build intothe system. Also, and as described elsewhere herein, the desired motionratio of the linkage affects the selection of the IC position, andtypically the shorter the linkage and closer the IC to the suspension,the less effectively the suspension's IC will track the Chain TorqueLine, and less effective the Brake Torque Isolation will be. To lowerthe percentage of anti-squat, the IC needs to be further out (toward orbeyond the front wheel); to increase the percentage of anti-squat), theIC needs to be closer to the rear wheel. Motion ratio is improved byselecting a rocker arm length close to that of the lower swingarm. Toprovide desirable Brake Torque Isolation performance, the rear of thelink must permit brake loads to be imposed at near 90 degrees (nearlyperpendicular) as described elsewhere herein;

[0060] using that selected location as the origin, projecting from thatorigin to select upper and lower axes for the frame members of a 4-bar(or other) suspension linkage. For 4-bar linkages utilizing the methodof the invention, the lower rear pivot needs to be sufficiently close toa line between the rear axle and the center of the crank to avoid havingthat pivot hit by standard (off-the-shelf) derailleurs; the front lowerpivot similarly needs to be sufficiently low to avoid being hit by anyfront derailleur and to ensure that the derailleur can be mounted atall, and sufficiently high to avoid excessive width behind the bottombracket area (which width might, for example, cause mud to excessivelycollect and block the rotation of the tire in adverse conditions).Persons of ordinary skill in the art will understand that there are manyother clearance issues in this area of frame and bicycle design, to makesure that the parts (especially those that move) do not undesirably rub,hit, or otherwise interfere with one another. The lower pivot locationsmust also be out of range of the rear derailleur to avoid “chain slap”(contact between the chain and the suspension structure, such as occursin the many current art designs (Specialized, GT, AMP, etc.));

[0061] selecting the location for a shock absorption member. Thislocation is preferably chosen so that standard (off-the-shelf) shocksizes can be used, and preferably to permit using a shock withsufficiently long stroke to keep the motion ratio low (as discussedherein) and to avoid excessive loads. Preferably, the shock is locatedand configured within the linkage so that the angles of the shock inrelation to the linkage provide for a linearly progressive or straightrate motion ratio;

[0062] selecting the lengths of the various linkage arms (some of thepreceding section also relates to selecting the lengths of the linkagearms). In the preferred embodiment, particularly the length of the upperlink (between the upper pivot points) is based on the desired travel(total movement up and down of the linkage) for the linkage as well asthe desired motion ratio of the suspension (which may, for example,allow for a broad selection of shock mediums). In addition, the design(including the linkage arm lengths) needs to take into accountstructural forces such as where various loads will intersect the frontstructure (such as elements 1-4 in FIG. 1). For example, loads appliedin the middle of the seat tube 1 may lead to premature failure of thattube 1 under extreme loading situations. In the preferred embodiment ofthe instant invention, linkage arms (and their associated force loads)attach close to tube intersections of a generally conventional “fronttriangle” (such as represented by elements 1-4 in FIG. 1), to utilizethe strength of those intersections. The amount of linkage travel can beadjusted by manipulating the ratio between the length of the front (ornose) of the rocker (the length of arms 6, 7 from pivot F forward) andthe rear of the rocker (the length of arms 6, 7 from pivot F back topivot E). Also, in 4-bar linkages such as the preferred embodiment, thelength and location of this upper swingarm must be carefully coordinatedwith the length of the other suspension structural members to achievethe desired amount of BTI (Brake Torque Isolation geometry). Asdiscussed herein, the angle between the suspension structural membersattached to the upper rear pivot can directly affect and determine theBTI of the suspension. If the upper linkage arm is too short, not onlywill the suspension IC not closely track the chain torque line, thesuspension will not provide desirable BTI geometry to reduce oreliminate problems from brake torque loads. Such brake torque loadproblems are very common in current four-bar linkage designs (includingthe TRUTH shown in FIGS. 13 a-c, GT STS/LTS designs, Specialized FSRdesigns and others);

[0063] generally, from the beginning or from this point on, CAD(computer-aided design) modeling of a myriad of configurations can helpdetermine the best possible configuration to achieve a desired balancebetween the elements of the design. Among other things, CAD modeling ofloads and torques can help determine a desirable configuration toestablish and maximize ICTT of the chain torque, the closest possibleBTI geometry to reduce or eliminate the effects of Brake Torque on asuspension linkage, maintain a near-vertical wheel travel path, keeplinkage motion ratio and shock motion ratio in the desired range, andselect the packaging, complexity of manufacture and ability to utilizeindustry standard parts;

[0064] design the parts. The rockers (the upper swingarm), being longand low (the rockers' position is preferably low relative to mostcurrent art, which allows the bike of the invention to have a lowstandover height with a relatively large amount of travel), preferablymaintain good stiffness torsionally from wheel twisting loads on thelinkage. The preferred embodiment and method further includes aone-piece machined swingarm yoke and a shockstay clevis machined from asolid piece of material, to help maintain near-perfect alignment andexcellent strength. Also, the “Rocker Block” (see FIG. 2J) helpsmaintain a desired amount of rigidity in the upper rocker arms withoutinterfering with or contacting the tire and seat post (which movebetween the rocker arms while the linkage is in motion).

[0065] In addition to providing a solution to each of the variousproblems discussed above (many or all of which could be utilized in asuspension design without the other elements of the invention), thevarious solutions can be practiced in a variety of combinations witheach other, and are preferably all included in the preferred embodimentand methods. Our preferred design is also very light and simple, whichminimizes the disadvantages of weight (indeed the preferred embodimentof the 7″ travel Dare weighs between 15%-50% less then it's nearestcompetitors. Literally, it is the lightest 7″ travel FS bike in theworld today. In fact the Dare weight is comparable to the shorter 4″travel cross country offerings of Specialized, Turner, GT and Intense),but even more importantly, our design greatly reduces or eliminates the“power sucking” of chain torque and other loads that occur with priorart designs, as discussed above.

[0066] We sometimes refer to the invention as Instant Center TrackingTechnology (or “ICTT”). We created and developed ICTT to eliminate theforegoing suspension design problems. In its preferred embodiment, ICTTis characterized by a four-bar linkage with specifically positionedpivot points and one or more shock absorption elements, resulting inimproved performance through, among other things, desirable alignment ofvarious force and torque lines over the range of expected rider loading,pedaling, and shock impacts.

[0067] Other objects and advantages of my invention will be apparentfrom the following specification and the accompanying drawings, whichare for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] All of the drawing figures filed herewith and discussed hereinare simply representative illustrations of the current preferredembodiment of the invention. Persons of ordinary skill in the art willunderstand that a wide variety of other embodiments can be utilized topractice the invention.

[0069]FIG. 1 is a side elevation view of a preferred embodiment of theinvention, but without a seat, a steering wheel, or a shock absorptionelement (although the words “shock unit” indicate its preferredlocation). Preferred dimensions and angles are shown for the linkage infully compressed position, although those of ordinary skill in the artwill understand both that the proportion of the numbers to each other isthe most critical thing and that the range of dimensions and anglescovered by the invention is much broader than just the one illustratedin these Figures and includes the range of angles and dimensions closerto those illustrated than any prior art device or method;

[0070]FIG. 1A is a partial, enlarged, broken side elevation view similarto FIG. 1, but illustrating further details regarding the preferredbrake assembly and alignment thereof. Although a cantilever,cable-actuated brake is illustrated, persons of ordinary skill in theart will understand that other brake mechanisms can be utilized; amongothers, a disk brake on the shockstay member will benefit from using theinvention's BTI geometry (said another way, the invention can bepracticed using disk brakes, among others). Among other things, suchpersons of ordinary skill in the art will understand the assembly andfunction of the indicated brake pad and cantilever with the shockstayassembly (FIG. 2G);

[0071]FIG. 2 is a side elevation view similar to FIG. 1, but emphasizesthe brake torque isolation geometry at various points of compression ofthe shock absorber. FIGS. 2A-2C are all similar to FIG. 2, but each one“breaks out” a single one of the compression stages (“laden” [2A],mid-point [2B], and full compression [2C]) shown in FIG. 2. Among otherthings, these Figures illustrate how the invention reduces or eliminatessquat or “jacking” under a wide variety of loading conditions; prior artsuspension designs that use small rockers or links of greatly unequallength (perhaps to maintain the traditional rear “triangle” appearanceof a bicycle) or otherwise differentially size the suspension pivotingelements cause the brake force resistance plane and the instant centerto move greatly in relationship to the drive chain line, causing lessdesirable performance than can be accomplished with the instantinvention. As shown in the drawings, the present invention's rocker armsare approximately the same length as the lower yoke or “swing arm”;

[0072]FIG. 2D is a partial, enlarged, broken side elevation view similarto FIG. 2A;

[0073]FIG. 2E is a top view taken along the broken line 2E-2E of FIG.2D, illustrating the preferred upper swingarm assembly or rocker arms;

[0074]FIG. 2F is a side elevation view taken along the broken line 2F-2Fof FIG. 2E;

[0075]FIG. 2G is an end view taken along the broken line 2G-2G of FIG.2D. This assembly preferably includes the “shockstay clevis” (FIG. 21)(preferably designed and fabricated from suitably strong, lightweightmaterial, to carry various structural loads and maintain desired linkagealignment for the upper swingarm or rockers (see FIG. 2E)), which“shockstay clevis” is preferably welded or attached to tubular materialextending downwardly to a “dropout” portion (the lower,forward-extending portion in which the lower rear pivot D is located) ofthe shockstay assembly (FIG. 2G). The “dropout” is also preferablymachined to help maintain alignment of the pivot and wheel axle mountingarea;

[0076]FIG. 2H is a side elevation view taken along the broken line 2H-2Hof FIG. 2G, illustrating the preferred “shockstay assembly”;

[0077]FIG. 2I is an end view similar to FIG. 2G, but illustratingspecifically the “shockstay clevis” (the “horseshoe” shaped upperportion) of the assembly of FIG. 2G. As indicated above, the clevis ispreferably machined from one piece of any suitably strong, lightweightmaterial capable of providing the desirable tolerances for rockermounting and brake stud location. The clevis also provides both verticalreinforcement and horizontal strength from torsional loads, helping tospread any twisting or compressive forces, especially as those. forcesare commonly encountered on the extreme terrain for which the bike's usewas intended;

[0078]FIG. 2J is a top view isolating the spacer clevis element or“reinforcement block” or “Rocker Block” of FIG. 2F. Together with theshockstay clevis (see FIG. 21), this block helps provide lateral andtorsional strength for dynamic loads induced by the contact patch of therear wheel against the ground. These forces occur regularly during thebike's use, such as during cornering or G-Outs (which can be caused byjumping or extreme terrain riding). Among other things, the “RockerBlock” is preferably fabricated from a single piece of strong,lightweight material, and shaped with ends each having a radius thatmatches the inside surfaces of the rocker arms 6, 7 against which thoseends mate (see below). The block is preferably attached to each rockerarm using two 6-mm screws (for a total of four screws, two on each end),although persons of ordinary skill in the art will understand that awide range of reinforcement devices and attachment means therefor can beutilized to provide the desired stiffening and support. Among otherthings, the stiffening block could even be cast as an integral part ofthe upper rocker arms assembly. The “Rocker Block” is preferablydesigned in a diamond cross-section (see FIG. 2L) to provide as muchtorsional strength as possible without contacting the seat tube or tirewhen the suspension is fully compressed (for example, see the locationof the rocker block on FIG. 1 showing the linkage in fully compressedposition). The rocker block is preferably removable to, among otherthings, allow the assembly to be removed and serviced. As indicatedabove, it would be possible to make the rocker block one piece with bothrocker arms, but the two nose sections of the rocker assembly (extendingforward toward the front wheel, on opposite sides of the bike) wouldstill preferably be formed or fabricated so as to taper toward eachother. Without such tapering, the nose section of the assembly may betoo wide and rub or contact the riders legs causing injury or irritationto the rider;

[0079]FIG. 2K is a side elevation view taken along the broken line 2K-2Kof FIG. 21, further illustrating the preferred “shockstay clevis”;

[0080]FIG. 2L is a sectional view taken along the broken line 2L-2L ofFIG. 2E, further illustrating the preferred “rocker block”;

[0081]FIG. 3 is a side elevation view similar to FIG. 1, butillustrating the nearly vertical wheel travel path achievable with theinstant invention. As explained elsewhere herein. anything less thanpurely vertical travel is generally less then optimally effective inabsorbing a bump, and/or has the effect of pulling the bike and riderunnecessarily back toward the bump. This problem becomes more noticeableas greater compression “travel” is permitted within the suspension. Forexample, the problem is very noticeable in most current art designshaving 5+inches of suspension travel. Some current art suspensions witheven less then 5″ travel do not keep wheel travel close to vertical;

[0082]FIG. 3A is similar to FIG. 2 (it includes only the two linkagearms adjacent the dark axis lines in FIG. 2), illustrating the nearlylinear shock motion ratio achievable with the instant invention;

[0083]FIG. 3B is an enlarged version of the dimensional movementinformation shown in the lower left corner of FIG. 3A (the numbers showinches of wheel movement—0.823 for the first quarter inch of shockcompression, 0.808 for the next quarter inch, etc.—as well asillustrating the provision of nearly 7 full “usable” inches of wheelmovement provided by the preferred embodiment). Persons of ordinaryskill in the art will understand that the benefits of the invention canbe enjoyed in a wide range of “travel” for a suspension (other than justthe 7″ just described), that the IC tracking disclosed herein greatlyexpands (beyond current art) the range of wheel travel that can beprovided without substantially compromising the handling andsluggishness of the bike ride, and that current shock absorbertechnology for bicycle embodiments of the invention provides somepractical “limit” on the amount of “travel” that may be readily providedin a bike without degrading the performance, prematurely wearing out theshock, etc. As those shock absorber technologies evolve, the practicalrange of “wheel travel” should correspondingly expand, using theinventions disclosed herein. As discussed and illustrated herein, thepreferred embodiment provides a slightly decreasing motion ratio as therocker arm is compressed. Among other things, this means that the “ride”typically gets more stiff in proportion to the amount the wheel iscompressed from its normal laden position. In other words, the furtherthe wheel suspension is compressed (the further the wheel “travels” incompression), which can be directly related to the degree of extremenessof the terrain and/or the bike's speed over a given terrain, a slightlyincreased spring rate or “stiffer” ride is provided (and is generallydesirable under those conditions, but it is only slightly, as thecurrent art suspension systems offer some radically increased springrates resulting in inhibited suspension function during extreme riding,which is not desirable);

[0084]FIG. 3C is a graph based in part on the information illustrated inFIGS. 3A and 3B, illustrating the shock force performance that can beprovided by using a 600 in-lb. shock spring with the preferredembodiment, and comparing that performance to other suspension designs.Persons of ordinary skill in the art will understand that the “600” isonly illustrative, that it means it takes 600 lbs of force to compressthe shock 1 inch, and that for mountain bikes such as illustrated in thepreferred embodiment, off-the-shelf shock absorber ratings are typicallyin the range of 200-800 in-lbs. Although the preferred embodiment curveapproaches “linear progressivity”, it is slightly and gradually curved.Typically, the flatter and smoother the curve, the larger the usefulrange of compression distance for the shock member (the instantinvention provides a much greater useful range in this regard than doprior art constructions). To desirably increase the compressionresistance as the wheel becomes more compressed (in other words, toprovide greater resistance to compression as larger “bumps” areencountered), the curve should slope upwards slightly from left toright, as does the curve for the instant invention;

[0085] FIGS. 4A-C are side elevation views similar to FIGS. 2A-C, buteach illustrating the “instant center” for a given amount of compression(4A illustrates full compression, 4B a mid-point of compression, and 4Ca “laden” or rider-mounted compression), as well as the alignment ofexemplary chain torque lines for various gear selections during theindicated amount of compression. In the preferred embodiment, the IC isinitially in exact alignment with the average chain torque line (whenthe suspension is in its normal, laden position). Also preferably, thatinitial IC position is in front of the bottom bracket or crank center ofthe bike (as just mentioned, on that “average” torque line) andpreferably is spaced correctly on that line to provide a desired amountof anti-squat performance. Although aspects of the invention can bepracticed if the IC is on or below ground level (such as alignment ofthe IC on the chain torque line, etc.), the preferred embodiment keepsthe IC above ground level in order to (among other things) provide theanti-squat performance and benefits described herein. This preferredinitial IC positioning is not found in any prior art of which theinventors are aware. The average, minimum, and maximum chain torquelines remain roughly constant for any bike design (or chain drivensuspended drive wheel system) that uses current “off-the-shelf” drivetrain components. Any chain-driven or shaft-driven system can benefitfrom the tracking of the IC, however, if that chain or shaft torque issusceptible to being “canceled” or reduced by the proper alignment ofthe IC. Among other things, the invention provides a ratio or percentageof torque line movement about the IC that is smaller for any selectedgearing combination than in prior art systems, resulting in lowered oreliminated chain torque reaction from the suspension linkage in any onealigned gear, or range of gears. Note that the drawings show the chaintorque line of a set of typical XC (cross-country mountain bike) gears.Such gears physically diverge more than a typical set of DH (down-hill)gears, and embodiments of the invention for various applications (XC,DH, or others) thus can include an application-specific shockstay orother components to further improve the performance of the invention forthat particular gear set (such as to locate the instant center evencloser to the DH or other gear set average chain torque line). Note alsothat several of the illustrated compression/chain torque combinationsare unlikely to ever occur during use of the bike. For example, it isunlikely that minimum chain torque (see the right, lowermost line inFIG. 4A) will occur while the wheel is at its maximum compression (whichmaximum is controlled by the shock absorption member);

[0086] FIGS. 5A-C are similar to FIGS. 4A-C, but instead each shows asingle gear chain torque line (lowest gear, average gear, and highestgear) and illustrates how the instant center moves with respect to eachof those lines during compression of the suspension from a laden, to amidpoint, to a fully compressed state. As with FIGS. 4A-C, note thatseveral of the illustrated compression/chain torque combinations areunlikely to ever occur during use of the bike;

[0087]FIG. 6 is a side elevation view similar to FIG. 1, butillustrating some of the anti-squat characteristics of the preferredembodiment;

[0088] FIGS. 7-12 illustrate (in very crude, not-to-scale, stick-figureform) some of the broad concepts incorporated in prior art designs; FIG.13A-C are similar to FIGS. 2A-C, but show a bike frame (named “TRUTH™”already marketed by one of the instant inventors (Mr. Ellsworth);

[0089]FIG. 14 is similar to FIG. 5B but illustrates Mr. Ellsworth'sTRUTH bike frame, and FIGS. 14A-C each “break out” and correspond to oneof the three compression states shown in FIG. 14. Persons of ordinaryskill in the art will understand that the chain drive lines in FIGS. 14and 14A-C are chain torque drive lines for average gearing selections;and

[0090] FIGS. 15-21 illustrate (in very crude, not-to-scale, stick-figureform) some of the many alternative embodiments of the invention, each ofwhich incorporate certain of the beneficial aspects of the invention.Within those Figures, persons of ordinary skill in the art willunderstand that the suspended portion of the bike frame is illustratedas being to the right in each figure, the suspension to the left, andthe shock absorbing member generally as a squiggly line (sometimes 2 areincluded within a single figure to illustrate alternative locations forthe shock). FIG. 15 shows the shock rigidly mounted from above andcompressed from the lower swingarm. FIG. 16 and FIG. 18 show similarembodiments which utilize a pull shock configuration with the shockmounted similarly to FIG. 15 in location but rigidly mounted at thebottom and pulled in compression of the linkage by its mount from theupper swingarm or rockers. FIG. 19 shows the shock mounted in either oftwo forward positions. FIG. 20 and 21 show the shock compressed by amidpoint mount along the upper swingarm. While most of the alternativeembodiments share some characteristic of current art, none of thecurrent art using the shock mounting locations shown currently alignsthe linkage to track the chain torque line with the linkage's IC, ortake advantage of other (or certainly all) elements of the instantinvention.

[0091]FIG. 22A and B illustrate a graph and a related table of datadepicting the relationship of various features of the preferredembodiment of the invention in relation to features of other bikesuspension systems of which the inventors are aware. The top graphillustrates the relationship of the difference between the instantcenter (IC) and the chain torque line (CT) versus the percentagecompression of the suspension system.

[0092]FIG. 23A and B illustrate a graph and a related table of datadepicting the relationship of the ratio of the difference between theinstant center (IC) and the chain torque line (CT), and the distancefrom the midpoint of a line between the upper and lower two rearwardpivots to the instant center (ICd) versus the percent compression of thesuspension system.

DESCRIPTION OF PREFERRED EMBODIMENT

[0093] In the preferred embodiment of the invention, as illustrated inFIGS. 1-6, the suspension is constructed to provide important anddesirable benefits and improvements over current suspension shockabsorber devices, constructions, and apparatus.

[0094] The various components of the invention may be fabricated in awide variety of ways and from a wide variety of materials, all of whichwill be readily understood by persons of ordinary skill in the art.Among other things, it is preferable that strong, lightweight materialsbe utilized, to reduce the energy required by the rider during riding aswell as during other transportation of the bicycle (such as loading ontobike racks, etc.).

[0095] In FIGS. 1-6, the suspension apparatus of the inventionpreferably includes a forward bicycle frame assembly consisting of aseat support tube or assembly 1, upper frame tube (“top tube”) 2, lowerframe tube (“down tube”) 3, fork support tube (“head tube”) 4, and crankaxle housing tube (“bottom bracket shell”) 5 welded together into aroughly triangular construction. Among other things, however, the frontof the bicycle may be configured in any of a myriad of ways to support alinkage designed to cancel chain torque using an instant center trackingand cancellation as described herein. For example, one currentlypopularized configuration is that of a “Y” design, and FIG. 21illustrates how such a design might incorporate the benefits of ICtracking set forth herein. Persons of ordinary skill in the art willunderstand that this portion of the bicycle frame is shown herein as the“suspended” portion, in that it is suspended from direct impacts on therear wheel, as described more thoroughly below.

[0096] Front and rear wheels 20 and 30, respectively, are shown, but noseat or steering wheel handle is shown (FIG. 6 does include a sketch ofa seat member). Persons of ordinary skill in the art will understandthat certain wheel spokes have been conveniently omitted from thedrawing that would exist in the actual preferred embodiment.

[0097] The rear wheel suspension portion of the suspension preferablyincludes two upper rocker arms 6 and 7 (element 7 is directly behind andhidden by element 6 in FIG. 1, but is preferably the mirror image ofelement 6 on the opposite side of the bicycle) pivotably engaged withthe seat tube 1 at point F, near the respective midpoints of rocker arms6 and 7.

[0098] The rear wheel suspension portion further preferably includes ashock absorber member (not shown, but indicated as positionedapproximately through the area labeled “shock unit” on FIG. 1A, forexample) pivotably attached at one end to a point A on an extension ofthe crank axle housing tube 5 (forward of the seat tube junction) and atthe other end to point B near the front of the two upper rocker arms 6and 7. The effective lengthwise axis of the shock absorber is bestillustrated by imaginary line J in FIG. 1A. Persons of ordinary skill inthe art will understand that although FIGS. 1-4 do not show the shockabsorber that is located between mounting pivot points A and B, theshock absorber may consist of any suitable shock absorbing construction,such as a wire coil, elastomer, air or other medium spring with an oil,air or other medium damper, or any other suitable expedient.

[0099] Persons of ordinary skill in the art will understand that theshock member can be attached in a wide variety of locations andorientations in alternative embodiments of the invention. By way ofexample and not by way of limitation, the shock member can be attachedbehind the seat, connected between the shockstay and rockers, on thedowntube, pulling or pushing, etc. as shown in the exemplary alternativeembodiments of FIGS. 15-21.

[0100] The rear wheel suspension portion further preferably includes alower yoke 8 which is pivotably attached at a point C near the top ofthe crank axle housing 5, and includes a rear wheel attachment uprightassembly 9 which retains the rear wheel 30 (rotatably mounted on a wheelaxis K). The preferred rear wheel attachment upright assembly 9 ispivotably attached to the rearward end of the lower yoke 8 (at theaxis/point D, which axis is defined by a line extending perpendicularlyin and out of the page at point D). The preferred rear wheel attachmentupright assembly 9 also is pivotably attached to the upper rocker arms 6and 7 at the axis E (extending perpendicularly in and out of the page atpoint E).

[0101] The attachment and alignment of pivot points D and E of the rearwheel attachment upright assembly 9 relative to the mounting of thebrake caliper (see FIG. 1A) on that wheel is important to provide thedesired brake torque isolation of the invention. All, or almost all,caliper brakes mount and function identically in the bicycleindustry-they all must squeeze the rim in the same place, which createsa torque at that point which is then transferred into the frame at theconnection points of the member on which they are mounted (for example,the shockstay 9) to the lower and/or upper swingarms (members 6, 7, and8 in the preferred embodiment illustrated herein). As discussedelsewhere herein, if that force is aligned at a 90 degree angle, thenthere is no torque, and that force has no impact on the compression orextension of the suspension, etc. Any deviation from 90 degrees createsa torque moment that will pull or push the swingarms up ordown-resulting in compression or extension of the suspension. Asdiscussed elsewhere, such compression can make the suspension too stiffso that it won't properly absorb bumps, or can even cause the tire tobreak loose from the ground and lose traction (this is called “brakechatter”). If the moment causes the suspension to extend, that extensiontends to lift the back of the bike, shifting the rider and weightforward and tending to “catapult” them over the handlebar and off thebike. None of these effects is conducive to good control of the bike.

[0102] The invention's preferred nearly-perpendicular orientation of themounting of the brake caliper to the line drawn between the rear lowerlink pivot D and the rear rocker pivot E helps prevent the suspensionfrom responding to the torque of an applied brake mounted on the rearupright or shockstay 9.

[0103] Persons of ordinary skill in the art will also understand thatmany of the invention's aspects in the preferred embodiment are (as inany design) the result of accommodating a wide variety of factors.Examples of such factors include providing the perpendicularity of afully compressed shock member as described elsewhere herein, whileproviding for a low standover height on the frame for smaller riders.Additionally, persons of ordinary skill in the art will understand that17.5 inches is within a current industry range for swingarm length, andalthough the invention can be practiced with swingarms of greater orlesser length, the handling and other considerations described hereinmake it preferable to try to accomplish the foregoing within a sub-17.5″swingarm length. If that dimension were too short, the rear wheelinterferes with the drive train components. If it is too long, thedriven tire won't maintain traction while climbing because, among otherthings, the rider's center of gravity is not sufficiently located overthe rear tire. Too long also adversely affects handling; among otherthings, the bike would have a wider turning radius and thus take agreater distance to turn.

[0104] The relative dimensions, shapes, and attachment points of therear suspension linkage components are among the factors that determinethe angle of the upper rocker arms 6 and 7 with respect to the loweryoke 8. Persons of ordinary skill in the art will understand that thedimensions (illustrated in inches) and the angles (illustrated indegrees) shown in the Figures are merely illustrative, as mentionedelsewhere herein. A wide variety of suspensions can utilize aspects ofthe invention, even without incorporating the specific dimensions andangles shown in the Figures.

[0105] The lower yoke 8 and the upper rocker arms 6 and 7 pivotablyattach to the forward frame assembly at pivot points C and F,respectively, and pivotably attach to the rear wheel attachment upright9 at the pivot points D and E, respectively.

[0106] As best shown in FIGS. 4A-C, 5A-C, and 6, imaginary lines(respectively drawn (1) along the lengthwise axis of upper rocker arms 6and 7 and (2) along the lengthwise axis of the lower yoke 8) converge onan imaginary forward point in space. As described herein, that point iscalled an “instant center”, labeled “IC” in the drawings. As the riderload and shock loads vary during the ride, the rear suspension's upperrocker arms 6 and 7 and lower yoke 8 (and consequently the rear wheel30) pivot radially about this “instant center”. For any given embodimentof the invention, the precise position of the instant center at anygiven moment in time depends on a number of factors, including (by wayof example) the location of the linkage's pivot points C, D, E, and F,the length of the rocker arms and lower yoke, and the amount ofcompression of the shock absorber.

[0107] The rocker and yoke pivots C, D, E, and F are preferablypositioned so that the “instant center” very closely approaches or (inthe best condition [such as in the laden condition of the preferredembodiment]) coincides with the driving axis of the drive chain (shownas various lines in FIGS. 4A-C and 5A-C), through a broad range ofcommon loading conditions from the force applied to the pedals. Arrowsand dimensions in FIGS. 4A-C and 5A-C illustrate the perpendicular“moment arm” for each of the situations, and where the drive chaintorque line exactly coincides with the IC, there is no moment arm andtherefore no chain drive torque to “suck” the rider's energy. This isillustrated, for example, in the laden condition of the preferredembodiment, in FIGS. 4C and 5B, both showing that condition for theaverage gear selection chain torque line. This “no-torque” condition isalso illustrated in FIGS. 4A and 4B, whereby at any point of compressiontravel for the suspension, a gear between the maximum and minimum gearshould be selectable to either “hit” the IC or get very near to it (inboth FIGS. 4A and 4B, a gear between the “average” and the “minimum”force would approach or “hit” the IC; by selecting and designing thesuspension using the invention disclosed herein, another embodiment ofthe invention can be structured in which compressed conditions wouldinstead “hit” the IC by selecting a gear between the average and theMAXIMUM gear chain torque lines; indeed, the invention permits the ICtracking and related performance parameters to be controlled veryprecisely). In such situations, all of that energy that would have been“sucked” into torque can instead be channeled into force moving thebicycle and rider forward (up or down the mountain, for example).

[0108] Even when the drive chain axis does not precisely intersect theIC (and there is therefore some torque-induced loading), that loading isgreatly reduced when compared to current art suspension devices andconstructions. Said another way, because of the close proximity to thechain torque line of all gear combinations, if the torque were to effectthe linkage, it would have a shorter distance to move the suspensionapparatus in order to align the IC with the CT, thus eliminating anypower loss.

[0109] Also, in the maximum compression position(see FIG. 1, forexample), the perpendicular relationship between the shock absorber axisand the rocker nose provides a desirable linearly progressive shocksuspension ratio (see FIGS. 2D-F and FIGS. 3A-C), while still isolatingpedal and brake forces (eliminating energy-absorbing torque loads).Persons of ordinary skill in the art will understand that the “nose” ofthe invention can be of a variety of shapes, dimensions, andconfigurations, and that the particular selection of the nose designwill (among other things) “program” the shock motion ratio behavior ofthe frame.

[0110] The precise range of movement of the instant center in thisregard can be selected by varying locations of pivot points C, D, E, andF (by, for example, varying the relative size and shape of thecomponents of the linkage), but the best embodiments of the inventionkeeps the instant center as close as possible to the chain drive torqueline during the greatest range of loading conditions, while maintainingcorrect geometry for BTI and anti-squat and keeping the packaging(design) conducive to using industry standard components, adaptabilityto a broad range of frame sizes, and a structurally light yet soundcomplete frame assembly.

[0111] Thus, when the drive chain axis intersects the IC, no drivechain-induced torque moment can affect, by compression or extension, thesuspension's shock absorber. Also, and as best illustrated in FIG. 1,the shock absorber (not shown) preferably has an effective lengthwiseaxis that is perpendicular to the axis of the rocker nose 12 during fullcompression of the shock absorber, helping to provide the beneficialmotion ratio (described and disclosed herein as preferably being alinearly progressive ratio). Persons of ordinary skill in the art willunderstand that the concept of a motion ratio at all, let alone theparticular shown within the preferred embodiment, is not necessary topractice and benefit from some of the other aspects of the invention.

[0112] This arrangement minimizes suspension-induced pedaling powerlosses caused by the drive chain moment-induced suspension movement.This loss is a primary loss of power transference efficiency in abicycle with rear suspension.

[0113] The torque interaction between the pedaling-induced wheel drivingforce and the ground can also cause rider-energy-wasting suspensioncompression due to a torque moment transferred to the shock absorbingmeans via the suspension upper rocker arms and lower yoke. To counteractthis moment, the suspension has approximately 10-20 percentanti-shock-absorbing means compression (or “anti-squat”) built into thesuspension geometry. As illustrated in FIG. 6, this percentage may becalculated by drawing an imaginary line through the center of the rearwheel tire contact patch and the “instant center”. Another imaginaryline is drawn through the bicycle and rider unit combination's center ofgravity, perpendicularly to the ground plane. The point where this lineintersects the imaginary line from the rear wheel tire's contact patchto the instant center is called the “anti-squat calculation point”. Theheight distance in units of measure of the “anti-squat” calculationpoint to the ground is divided by the height distance in units ofmeasure from the ground to the bicycle and rider unit combination'scenter of gravity. This number gives the percentage of “squatresistance” built into the rear suspension's geometry, where 100 percentequals full cancellation and zero percent is no cancellation.

[0114] The percentage of “anti-squat” resistance varies due to thedynamic changes of rider positioning during riding, anatomicaldifferences among riders and the amount of static “sag” or “droop” towhich the individual rider prefers to adjust his suspension. Amounts ofanti-squat higher than 30 percent cause suspension bind or resistance tobump movement during is pedaling, which is normally to be avoided ifpossible. Excessive “anti-squat” resistance built into the rearsuspension's geometry can also produce unwanted suspension liftingmoments during braking which reduces the rear suspension's ability toabsorb bump movements. To prevent unwanted suspension movement, bind orpreload under the forces of braking, the rear brake device (consistingof either a disc brake caliper or conventional bicycle rim brake)mounting point is attached to the rear wheel attachment upright. Theangle of the rear wheel attachment upright to the upper rocker armsstatically approaches 90 degrees in angle in a loaded condition, causingthe torque moment induced by brake forces to be transferred into theforward frame assembly laterally with minimal horizontal torquecomponent. This transfer of the brake forces thus will not have anextending effect or compressing effect on the shock absorber, leavingthe suspension free to move horizontally when activated by wheel bumpforces while the rear brakes are in operation. Positioning the rearsuspension's instant center relatively close to the ground plane alsohelps the rear suspension's bump compliance under braking.

[0115] Among other things, there are two forces that affect the braketorque action discussed herein. The primary brake torque force is thatof the transference of force via the shockstay member of the linkage.The secondary force is the wheel torque against the linkage, whichapplies to the anti-squat effect from the brake force (not the drivechain forces), which then relates to the IC in a manner similar to theway the drive torque affects the wheel torque. These primary andsecondary forces are similar to the drive torque problems discussed andaddressed herein (the primary drive torque “problem” force being thechain torque force, and the secondary being the wheel torque).

[0116] As compared to the “torque reactive” suspensions described above,the non-torque-reactive suspension or ICTT (Instant Center TrackingTechnology) aligns the suspension's instant center with the drive chainline of the average of the gear ratios, providing greatly improvedperformance. As indicated above, the instant center is described as thepoint in space where imaginary straight lines drawn through thesuspension's main pivot points intersect. This point is the imaginary orvirtual axis that the rear suspension pivots about. By having theinstant center aligned with the chain line on the drive or tensionedside, the cranks pulling on the chain during pedaling has no off centerleverage or moment arm to lift or compress the suspension. Due to theinstant center's positioning in relationship with the bicycle/ridercentroid of mass distribution, the rear suspension resists wheel-induceddrive torque moments that can also move the suspension. This is called“anti-squat” geometry, as discussed above. The suspension has between10-30% “anti-squat” (depending on the position of and individualphysical characteristics of the rider), allowing free, fully activesuspension movement under bump conditions but providing enoughresistance to reduce wheel-to-ground torque reaction induced suspensionmovement. Consequently, the suspension is fully active even under thehardest of pedaling loads, allowing the tires to maintain traction onthe roughest, steepest climbs. By having shock rocker arms of a lengthnearly equal to that of the lower yoke, the instant center follows thechain line closely throughout the suspension's entire stroke. Becausethe shock rockers and lower yoke are close to the same effective length,and due to the location of the pivots (C, D, E, and F), the wheelfollows a nearly straight up and down path, keeping the wheel base closeto constant, eliminating pedal kickback while hitting bumps whilepedaling and reducing chain whip for more positive shifting. Due to thenear vertical wheel path, the shock absorbing action is also moreefficient as the wheel is displaced only upward (not forward) whenencountering a bump.

[0117] As described above, the “instant center” is preferably locatedexactly on the average chain torque axis in the suspension's ladencondition (as indicated elsewhere herein, “laden” condition is thenormal operating position of the suspension linkage as set up by theindividual rider). Chain-induced torque reaction is eliminated any timethe suspension's instant center is aligned with the drive-chain line.Also, the wheel drive torque reaction between the tire and the ground issimilarly reduced and controlled through anti-squat geometry asdescribed above. The preferred embodiment results in the desiredalignment of the instant center being held close to the chain line inall gear positions and suspension positions (rider load, shock load,etc.). Among other things, this results from the suspension linkage armsbeing nearly equal in length and going through nearly identical arcs asthe rear suspension goes through its stroke, as compared to the typicalprior art design of short upper and longer lower linkage arms. Thisgeometry helps keep the instant center from shifting lower inrelationship to the chain line as the suspension compresses (whichshifting is typical in certain prior art designs, for those prior artdesigns that even have an instant center at any time). The position ofthe brake anchor and suspension pivot points nearly eliminates brakingtorque reaction.

[0118] As a result, the preferred embodiment is completely or verynearly completely non-torque-reactive in a much greater range ofcommonly-used gears. All that remains is very slight, minimal torquereactivity in extreme, seldom-used gear combinations. Accordingly, atleast some of the extreme chain drive positions shown in FIGS. 4A-C and5A-C infrequently occur for most riders.

[0119] The preferred embodiment's instant center tracks the chain torqueline very closely, always within the range of gears and very near theaverage, most commonly used gears of the gear range, insuring minimaltorque reaction, regardless of the suspension's location in stroke. Therange of gear positions where the suspension is or is almostnon-pedal-torque-reactive is very large, far larger than any currentproduction bicycle, and/or the percentage of deviation (through theentire compression stroke, laden to fully compressed, etc.) fromcomplete torque cancellation is smaller than that of any currentproduction bicycle.

[0120] The invention's ability for the chain torque line to track theinstant center is illustrated in the graphs and data of FIGS. 22A, 22B,23A, and 23B. In FIGS. 22A and B, the difference between the instantcenter (IC) and the chain torque line (CT) is plotted as a function ofthe percentage of compression of the suspension system. When the instantcenter tracks the chain torque line perfectly, the difference betweenthe instant center and chain torque line is equal to zero. As is evidentin FIGS. 22A and B, the instant center of the preferred embodiment ofthe invention (such as the Truth 2000 model) tracks the chain lineperfectly when the suspension is approximately twenty to thirty-fivepercent compressed (i.e. the difference between the instant center andthe chain line is zero when the suspension is approximately twenty tothirty-five percent compressed, or when it is in its normally ladenposition). Furthermore, the maximum deviation of the instant center fromthe chain torque line is the lowest for the preferred embodiment of theinvention, indicating that the suspension system of the currentapplication “tracks” the chain torque line more accurately than anyother suspension system of which the applicants are aware. In fact, thedifference between the instant center and the chain torque line for thepreferred embodiment of the invention is less than 0.66 inches in the“uncompressed” state and is less than 1.46 inches in the “fullycompressed” state. Accordingly, the invention permits a tracking betweenthe instant center and the chain torque line of less than 1.46 inchesthroughout the suspension's entire compression range. Persons ofordinary skill in the art will understand that these numbers are relatedto the amount of travel or movement of the suspension apparatus, suchthat all current art is 6″ or less travel compared with one embodimentof the invention 7″ of travel. The Truth 2000 with 5″ of travel isnearer to zero then any current art. In addition, persons of ordinaryskill in the art will understand that fine-tuning adjustments of anyparticular bicycle may slightly affect the specific numbers shown inFIGS. 22A and 22B and 23A and 23B, but that the inventive principles andconcepts discussed herein still apply.

[0121] Although FIGS. 22A and 22B indicate that the Turner A. B. bicycleyields a similar maximum value of 1.46 (for the difference between theinstant center and the chain torque), as of this date, it is unclearwhether that Turner A. B. bicycle actually constitutes prior art withrespect to Applicants' invention. In any case, the Turner A. B. bicycledoes not teach or disclose how to achieve a maximum value lower than1.46.

[0122] As can also be appreciated from FIGS. 22A and 22B, the majorityof the bikes of which the inventors are aware never perfectly align theinstant center with the chain torque line. This is fully appreciated bymost of the bikes yielding values that remain above or below the zeroaxis throughout their entire compression ranges. When the value of theIC-CT is negative on the graph, the energy of the rider is wasted, asthe resulting forces push the rider's weight up rather than forward witheach pedal stroke. When the value of the IC-CT is positive, the forcestend to feed the chain torque into the shock absorber dissipatingenergy, that would have propelled the bike/rider unit forward, intoheat.

[0123]FIGS. 23A and 23B illustrates the relationship of the ratio of thedifference between the instant center (IC) and the chain torque line(CT), and the distance from the midpoint of a line between the upper andlower two rearward pivots to the instant center (ICd) versus the percentcompression of the suspension system. As can be appreciated, thepreferred embodiment of the invention (e.g. the Dare model) keeps theaforementioned ratio closer to zero than any other bicycle throughoutthe entire compression. In particular, the aforementioned ratio is lessthan 0.08 throughout the entire compression range of the preferredembodiment of the invention. This results in the maintenance ofconsistent anti-squat programming in the linkage system, as discussedabove.

[0124] Suspension action of the preferred embodiment of the invention isunaffected by pedal force input. The suspension of the invention isalmost completely non-brake-torque reactive under most suspension loadconditions. The mildly progressive, near-linear shock motion ratioprovided by the invention works well with a wide range of shockabsorbing elements, such as coil spring and air spring type shockabsorbers. The invention's near-constant wheelbase dimension insurespositive shifting and eliminates suspension-induced pedal kickback. Thenear-vertical wheel path (during shock absorption) insures efficientshock absorption and reduces forward drive energy losses. The inventionis a simple, elegant, rigid design.

[0125] Although bicycles incorporating the invention are more expensiveto manufacture than those having a non-suspended design, it willtypically be less than a lot of current art suspended designs (becausethe design is less complex and requires less materials, etc.), and thecost will be worth the improved performance for many, if not most,riders.

[0126] A method of shock absorption includes the steps of providing afour-piece linkage as described herein, which linkage is pivotal at fourpoints of connection forming the linkage, and providing a shock absorbermember mounted between two opposing members of that linkage, andimposing loads on the shock absorber. Further steps include providing alinkage of the aforementioned character in a bicycle construction,riding the bicycle, and traveling over rugged terrain. Those twoopposing members (such as the lower swingarm or yoke 8 and upperswingarms or rocker arms 6, 7, respectively) each have first and secondends and a middle portion therebetween. The shock absorber member ispreferably located relatively toward the first end, which first end isillustrated in the drawings as being toward the front end of thebicycle. In alternative embodiments the yoke 8 and rocker arms 6, 7might be positioned so that the rear wheel attachment upright assembly 9is pivotably attached to the middle portion of those components, and theshock absorber is rearward of the rear wheel attachment upright assembly9 (to some degree, the shock member can be mounted anywhere, althoughthe packaging really suffers with some choices of shock location), andin any case the shock absorber is preferably mounted in a spacedrelationship from the other two linkage members.

[0127] When developing the preferred instant center location, at leastthe following factors indicate that the IC should generally not be tooclose to the bottom bracket along the average chain line torque vector(the closer the IC, the more extreme the noted problems become):

[0128] 1. The closer the IC location, the shorter the upper link (orbellcrank) (corresponding to members 6, 7 in the preferred embodiment).The shorter the bellcrank, the more quickly and further the IC “dives”below the chain line as the suspension is compressed. This “diving”undesirably contributes to the aforementioned jacking effect under pedaltorque load, due to the torque moment created by the distance betweenthe IC and the chain line. In contrast to any such “close” prior artapproaches, the IC of the instant invention tends to better “track” thechain line under compression and not depart as far from that line. Forexample, and as shown in FIG. 5B, the IC of the preferred embodimentonly very gradually moves away from the average chain torque line as thesuspension becomes more compressed. Moreover, as shown in FIGS. 5A and5C, the preferred embodiment's IC actually moves closer to the chaindrive lines during the compression stroke, if the rider has selected themaximum or minimum gear arrangement. The suspension's particularperformance characteristics in this regard can be selected by the framedesigner, by using the inventive method and apparatus set forth herein.Although at first blush, certain prior art suspensions appear to provide(at least in certain stages of shock compression) a torque arm (andconsequent torque force) for the chain torque line that is less than theinstant invention, that “torque” sensation and force experienced by therider actually involves an additional “moment arm”: the distance betweenthe IC (functioning as a virtual pivoting axis) and the “mass” beingpivoted around that axis (the wheel, the suspension, etc.). In otherwords, the “torque” experienced by the rider (and the energy “wasted” or“sucked” away) is a function of both the aforementioned “mass” acting onits moment arm (the distance from that mass center to the IC) and thechain drive force acting on its moment arm. Thus, when the IC is moved“close” to the rear wheel, for example, the “mass” is easier to move(because its moment arm is shorter), and therefore the jacking, etc.caused by a given amount of misalignment of the IC from the chain torqueline is greater than if the IC were farther forward. Said another way,the effective energy “suck” or wheel movement would occur for an ICcloser to the rear wheel but having a proportionally shorter distancebetween the IC and the chain force line as for an IC “farther” out buthaving a proportionally longer distance between the IC and the chainforce line.

[0129] 2. An IC located in a “close” position would require a relativelyshorter upper link and would require a relatively shorter shockabsorber. Consequently, such “closer” IC designs have a very high motionration with a rapid change in rate (rising, falling) in any embodimentwhere the design packaging would be practical. Moreover, rapid changesin shock absorber piston velocity are difficult for the shock's valvingto handle accurately, and unduly wear out the shock member.

[0130] 3. A “close-in” IC necessitates locating the main load-bearingpivots (those that would correspond with C and F in FIG. 1, for example)more closely together along the seat tube 1. These pivots sustainextreme torsion loads during cornering and very hard pedaling. If thepivots are located too closely together, the seat tube 1 will be put inunsupported torsion. The main pivots C and F in the instant inventionare preferably sufficiently spread from each other (and/or arecorrespondingly close to the top and down tubes 2 and 3) so as not tocouple the seat tube 1 in torsion and to instead apply those loadsdirectly to the tubes that will better absorb them.

[0131] 4. The closer the IC, the more difficult it is to provide anupright (such as upright 9) with an operating range at or near theoptimal 90 degree angle to the upper rocker for brake torque reactionisolation.

[0132] 5. The closer the IC the higher the percentage of anti-squat thatcan add to the unwelcome jacking of the rear suspension under brakingand suspension function reducing bind of the suspension under pedalingloads.

[0133] Similarly, when developing the preferred instant center location,at least the following factor indicates that the IC should generally notbe too far from the bottom bracket along the average chain line torquevector (the closer the IC, the more extreme the noted problems become):

[0134] 1. The farther the IC is from the bottom bracket, the more thesuspension will act like a prior art parallel link suspension and thusbe subjected to unequal chain torque loads (where the chain location istypically closer to one pivot axes [generally the lower swingarm incurrent bicycle art] causing more torque loading on that axis, which canresult in “lock out” or upward “jacking” on the linkage) and will beunable to provide any desired anti-squat geometry, or the percentage ofanti-squat becomes so small as to be meaningless. Although this would bepreferable to having the IC set too closely in, the maximum “far”position for the IC is generally determined by packaging considerations,along with balancing all other design and performance elements (such asBTI and Anti-squat). As indicated above, “too close” is generally worsethen “too far”.

[0135] In contrast to the aforementioned prior art problems with “brakeinduced torque”, the ICTT rear suspension does not have a traditionalforward sloping seat stay tube; the preferred ICTT has a wheel retaining“upright” 9 instead. An angle of close to 90 degrees under load ismaintained from the rear upright to the upper rocker arm greatlyreducing the amount of torque transferred to the rear suspension. Due tothe location of the instant center, wheel braking forces are transmittedto near the bicycle's drive chain axis which, since it is fairly closeto the plane of the ground, cannot contribute to any significant jackingor squatting effect.

[0136] Unlike the above-described shock absorber motion ratio problemsthat exist in current designs, the ICTT rear suspension uses long rockerarms to maintain as close to linear shock motion ratio as possible. Theinvention's rocker geometry has a gentle rising rate that isaccommodating to bumps of all sizes and frequencies. The invention'sgentle rising rate works well with both coil spring and air spring typeshocks. With small shock rockers having a rapid change of shock rate,the shock absorber's valving (which affect the shock absorberperformance in compression and rebound) is subjected to very rapid shaftspeed accelerations. The longer shock rockers 6, 7 of the instantinvention lowers the typical shock shaft velocity, improving the shock'sdamping performance. At very high motion ratios, damping changes musthappen with very small shock shaft movements. The ICTT suspension'sgentle rising rate allows greater shock valve sensitivity due to themore constant shock shaft speed throughout the suspension's stroke.

[0137] Unlike the complicated designs of current bicycle suspensions,the ICTT rear suspension accomplishes all of its goals in a simple,stiff, rugged, lightweight package with a minimum of parts,flex-inducing pivots and excess complexity.

[0138] The apparatus and methods of our invention have been describedwith some particularity, but the specific designs, constructions andsteps disclosed are not to be taken as delimiting of the invention inthat various obvious modifications will make themselves apparent tothose of ordinary skill in the art, all of which will not depart fromthe essence of the invention and all such changes and modifications areintended to be encompassed within the appended claims.

We claim:
 1. A method of improving riding performance of a bicyclehaving a rear wheel suspension system, which comprises an upper rockerarm and a lower rocker arm, each rocker arm comprising rearward andforward pivot points, the method comprising the step of: tracking achain torque line with an instant center, thereby improving thebicycle's performance by reducing torque reactivity of the suspensionsystem, wherein the instant center is defined as a point at theintersection of a first imaginary straight line drawn through therearward and forward pivot points of the upper rocker arm, and a secondimaginary straight line drawn through the rearward and forward pivotpoints of the lower rocker arm, and wherein the instant center islocated in front of a front wheel axle, and above a horizontal lineextending through the front wheel axle when the suspension system is notcompressed, and a perpendicular distance between the instant center andthe chain torque line decreases to zero as the suspension is compressed,and wherein the chain torque line is defined as a parallel lineextending along the tension side of a chain while the chain ispositioned on chain sprockets of the bicycle.
 2. The method of claim 1,wherein the step of tracking a chain torque line with an instant centerreduces chain torque reactivity of the suspension system.
 3. The methodof claim 1, further comprising a step of reducing brake torquereactivity of the suspension system by positioning a brake about therear wheel of the bicycle so that braking forces created by the brakeacting on the rear wheel are nearly perpendicular to a straight linepassing through the rearward pivot points of the upper and lower rockerarms, thereby reducing brake torque reactivity of the suspension system.4. The method of claim 3, comprising a step of positioning the brake ona shockstay that has a receptacle to receive the rear wheel axle, andthat is pivotably connected to the rearward pivot points of each of theupper and lower rocker arms.
 5. The method of claim 1, furthercomprising the steps of: providing a rider on the bicycle, thecombination of the rider and the bicycle having a combined center ofgravity; and controlling compression of the suspension system bymaintaining a ratio of (i) a perpendicular distance from the ground to apoint where a line extending forward from a point where the rear wheelcontacts the ground to the instant center intersects a perpendicularline extending vertically through the combined center of gravity, and(ii) a perpendicular distance from the ground to the instant center,less than {fraction (3/10)}.
 6. The method of claim 1, furthercomprising the step of aligning the instant center with the chain torqueline so that the perpendicular distance between the chain torque lineand the instant center is zero at any point throughout the suspensionsystem's full range of compression.
 7. The method of claim 6, whereinthe perpendicular distance between the chain torque line and the instantcenter is zero when the bicycle is in a normally laden position.
 8. Themethod of claim 6, wherein the perpendicular distance between the chaintorque line and the instant center is less than 1.46 inches throughoutthe suspension system's full range of compression.
 9. The method ofclaim 6, wherein the instant center is aligned with an average chaintorque line, the average chain force torque line defined as a parallelline extending along the tension side of the bicycle's chain when thechain is positioned at a vertical distance from the center of theforward and rearward chain sprockets, respectively, wherein the verticaldistance is the average of the radii of the smallest and largest forwardchain sprockets and the average of the radii of the smallest and largestrearward chain sprockets.
 10. A method of improving riding performanceof a bicycle having a rear wheel suspension system, which comprises anupper rocker arm and a lower rocker arm, each rocker arm having aforward and rearward end, the method comprising the step of: tracking achain torque line with an instant center, thereby improving thebicycle's performance by reducing torque reactivity of the suspensionsystem, wherein the instant center is defined as a point at theintersection of a first imaginary straight line extending forward fromthe rear end, along the center, of the upper rocker arm, and a secondaryimaginary line extending forward from the rear end, along the center, ofthe lower rocker arm, and wherein the instant center is located in frontof a front wheel axle, and above a horizontal line extending through thefront wheel axle when the suspension system is not compressed and aperpendicular distance between the instant center and the chain torqueline decreases to zero as the suspension is compressed, and wherein thechain force torque line is defined as a parallel line extending alongthe tension side of a chain while the chain is positioned on chainsprockets of the bicycle.
 11. The method of claim 10, further comprisingthe step of aligning the instant center with the chain torque line sothat the perpendicular distance between the chain torque line and theinstant center is zero at any point throughout the suspension system'sfull range of compression.
 12. The method of claim 11, wherein theperpendicular distance between the chain torque line and the instantcenter is zero when the bicycle is in a normally laden position.
 13. Themethod of claim 10, further comprising a step of reducing brake torquereactivity of the suspension system by positioning a brake about therear wheel of the bicycle so that braking forces created by the brakeacting on the rear wheel are perpendicular to a straight line passingthrough the rearward pivot points of the upper and lower rocker arms,thereby reducing brake torque reactivity of the suspension system. 14.The method of claim 10, further comprising the steps of: providing arider on the bicycle, the combination of the rider and the bicyclehaving a combined center of gravity; and controlling compression of thesuspension system by maintaining a ratio of (i) a perpendicular distancefrom the ground to a point where a line extending forward from a pointwhere the rear wheel contacts the ground to the instant centerintersects a perpendicular line extending vertically through thecombined center of gravity, and (ii) a perpendicular distance from theground to the instant center, less than {fraction (3/10)}.